Shipyards have one or more dry docks with slots of time (continuous periods) reserved for the construction of vessels. The required slot time depends upon the steel production rate of the shipyard, which is the rate at which large steel sections can be welded together. Very large vessels with a hull steel weight of over 40,000 tons require a long period to build. It can require a long time and great difficulty to find sufficiently long slot times available in a dry dock for such large vessels. One prior art method for reducing the time in a dry dock is to fabricate only the vessel hull in the dry dock, and then float out the hull to a location where topside packages (equipment to be mounted on the hull) are installed, as along side a quay or dock. Although this reduces the required time in the dry dock, it does not reduce the time greatly because most of the time required to construct a complete vessel is the time for welding together plates to form the hull. The topside packages are usually pre-fabricated, and can be rapidly lifted into place and connected, provided that heavy duty cranes are available at the dry dock. A system for constructing a very large vessel, and especially a FPDSO complex (including Floating, Production, Drilling, Storage and Offloading Sections) using a minimum amount of time of a very large dry dock, would be of value. It would be even more useful if the different sections of the vessel could be constructed with greater expertise than at present.